1. Field of the Invention
This invention relates to semiconductor chip having protruding electrode and manufacturing method for the same, and multi-chip semiconductor device equipped with a plurality of semiconductor chips having protruding electrodes.
2. Description of Related Art
FIG. 20 is an illustrative sectional view showing the structure of a semiconductor chip having a conventional penetrating electrode.
This semiconductor chip 91 includes a semiconductor substrate 90 made of silicon (Si). On one surface (hereinafter, referred to as “front surface”) of the semiconductor substrate 90, a function device 71 having a plurality of electrodes is formed. By the side of the function device 71, a through hole 79 penetrating the semiconductor substrate 90 in the thickness direction is formed.
On the front surface of the semiconductor substrate 90, a hard mask 72 having openings 72a and 72b is formed. The hard mask 72 is made of silicon oxide (SiO2). In the vertical top plan view of the semiconductor substrate 90, inside the opening 72a, an electrode of the function device 71 exists, and the opening 72b and the through hole 79 form one hole having a continuous inner wall surface.
On the inner wall surface of the through hole 79 and the opening 72b, an insulating film 74 made of silicon oxide is formed. In a predetermined region including the surface of the insulating film 74, the inside of the opening 72a, and the surface of the hard mask 72 between the opening 72b and the opening 72a, a continuous diffusion preventive film 75 made of tantalum nitride (TaN) or titanium nitride (TiN) is formed.
The insides of the through hole 79 and the opening 72b are filled with a penetrating electrode 80. On the surface opposite the front surface of the semiconductor substrate 90 (hereinafter, referred to as “rear surface”), a rear side protruding electrode 82 protruding from the rear surface is formed integrally with the penetrating electrode 80. The penetrating electrode 80 and the rear side protruding electrode 82 are made of copper. The rear side protruding electrode 82 is formed so as to almost overlap the penetrating electrode 80 in the vertical top plan view of the semiconductor substrate 90.
The tip end part of the rear side protruding electrode 82 and the vicinity thereof are covered by a low melting point metal layer 83 made of a low melting point metal such as tin (Sn).
On the front surface of the semiconductor substrate 90, an interconnection member 81 that is made of copper and integral with the penetrating electrode 80 is provided on the penetrating electrode 80 and on the diffusion protective film 75 except for the surfaces of the through hole 79 and the opening 72b. The electrode of the function device 71 exposed to the inside of the opening 72a is electrically connected to the rear side protruding electrode 82 through the diffusion preventive film 75, the interconnection member 81, and the penetrating electrode 80.
On the interconnection member 81, a front side protruding electrode (bump) 78 made of a metal (for example, gold (Au)) is formed through a UBM (Under Bump Metal) layer 77 made of titanium tungsten (TiW) or titanium. The front side protruding electrode 78 is almost right above the penetrating electrode 80 (so as to overlap the rear side protruding electrode 82 in the vertical top plan view of the semiconductor substrate 90).
In this semiconductor chip 91, the interconnection length between the front surface side and the rear surface side of the semiconductor substrate 90 is shortened by the penetrating electrode 80 penetrating the semiconductor substrate 90.
Furthermore, in this semiconductor chip 91, electrical connection from the front surface side of the semiconductor chip 91 to the function device 71 through the front side protruding electrode 78 is possible, and electrical connection from the rear side of the semiconductor chip 91 via the rear side protruding electrode 82 is also possible. In detail, this semiconductor chip 91 can be joined to an electrode pad, etc., formed on a wiring board via the rear side protruding electrode 82. Furthermore, by layering semiconductor chips in the vertical direction and joining the front side protruding electrode 78 and the rear side protruding electrode 82 of the adjacent semiconductor chips, the semiconductor chips 91 can be electrically connected to each other.
When the rear side protruding electrode 82 is joined to an electrode pad, etc., formed on a wiring board, or the front side protruding electrode 78 of another semiconductor chip, by setting the temperature of the semiconductor chip 91 to be equal to or higher than the melting point (solidus temperature) of the low melting point metal forming the low melting point metal layer 83 for a proper period of time, a melt of the low melting point metal can be produced. Thereby, the rear side protruding electrode 82 and the electrode pad or the front side protruding electrode 78 of another semiconductor chip 91 are joined to each other via the low melting point metal layer 83.
FIG. 21(a) through FIG. 21(h) are illustrative sectional views describing a manufacturing method for the semiconductor chip 91 shown in FIG. 20. Such a manufacturing method is disclosed in Unexamined Japanese Patent Application No. 2001-53218.
On the front surface of a semiconductor wafer w (hereinafter, referred to as “wafer,” simply) having a function device 71 formed on the front surface, a hard mask 72 having openings 72a and 72b at predetermined portions is formed. Inside the opening 72a, the electrode of the function device 71 is exposed. Inside the opening 72b, a predetermined region of the wafer W in which the function device 71 is not formed is exposed.
Next, in the wafer W exposed inside the opening 72b, a concave portion 73 is formed by reactive ion etching (RIE). At this time, the opening 72a is closed by a resist so as to prevent the function device 71 from being etched. Next, an insulating film 74 is formed on the inner surface of the concave portion 73 by the CVD (Chemical Vapor Deposition) method. This condition is shown in FIG. 21(a). Next, on the entire exposed surface of the wafer W front surface side including the insides of the openings 72a and 72b and the inside of the concave portion 73, a diffusion preventive film 75 is formed (see FIG. 21(b)).
Then, on this diffusion preventive film 75, a seed layer made of copper (not shown) is formed, and then the entire exposed surface of the wafer W front surface side is supplied with a metal material (copper) 76 for forming the interconnection member 81, the protruding electrode 80, and the rear side protruding electrode 82.
Thereby, the insides of the openings 72a and 72b and the concave portion 73 are almost completely filled with the metal material 76. The metal material 76 is electrically connected to the electrode of the function device 71 exposed inside the opening 72a of the hard mask 72. The metal material 76 is also supplied to the outsides of the openings 72a and 72b and the concave portion 73 so as to be continuously disposed from the inside of the opening 72a to the insides of the opening 72b and the concave portion 73. This condition is shown in FIG. 21(c).
Next, by using a mask with a predetermined pattern, a portion except for a predetermined region including the concave portion 73 (opening 72b) and the opening 72a of the metal material 76 and the diffusion preventive film 75 in the vertical top plan view of the wafer W is removed by etching. This condition is shown in FIG. 21(d). Thereafter, as appropriate, a surface protective film for protecting the metal material 76 is formed so as to cover the metal material 76.
Next, on the metal material 76, in a region of the surface of the metal material 76 almost overlapping the concave portion 73 in a vertical top plan view of the wafer W, a UBM layer 77 and a front side protruding electrode (bump) 78 are formed in order (see FIG. 21(e)). When the metal material 76 is covered by the surface protective film, prior to formation of the UBM layer 77, the surface protective film is made not to exist in the region for forming the front side protruding electrode 78.
Next, the rear surface of the wafer W is dry-etched and reduced in thickness to be smaller than the depth of the concave portion 73. This step is performed by setting the etching rate for the insulating film 74 to be lower than the etching rate for the wafer W. Thereby, the concave portion 73 is formed into a through hole 79 penetrating the wafer W in the thickness direction, and the metal material 76 disposed inside the concave portion 73 serves as a penetrating electrode 80 that electrically connects the front surface side and the rear surface side of the wafer W.
Apart of the metal material 76 disposed inside the concave portion 73 becomes a rear side protruding electrode 82 protruding from the rear surface of the wafer W while being covered by the insulating film 74 and the diffusion preventive film 75. The remainder of the metal material 76 becomes an interconnection member 81 that electrically connects the penetrating electrode 80 and the electrode of the function device 71. This condition is shown in FIG. 21(f).
Next, the insulating film 74 exposed to the rear surface of the wafer W is removed by etching. Thereby, as shown in FIG. 21(g), the diffusion preventive film 75 covering the rear side protruding electrode 82 is exposed. Furthermore, the diffusion preventive film 75 covering the rear side protruding electrode 82 is removed by etching, and the tip end part of the rear side protruding electrode 82 and the vicinity thereof are exposed (see FIG. 21(h)).
Thereafter, on the exposed surface of the rear side protruding electrode 82, a low melting point metal layer 83 is formed by means of, for example, electrolytic plating, and the wafer W is cut into pieces of semiconductor chips 91 having the penetrating electrodes 80 shown in FIG. 20.
However, if such a semiconductor chip 91 is left in the atmosphere, on the surface of the low melting point metal layer 83 made of tin, etc., an oxide film is easily formed. The oxide film is not wetted by the melt of the low melting point metal, so that the area that substantially contributes to junction between the rear side protruding electrode 82 and an electrode pad or the front side protruding electrode 78 of another semiconductor chip 91 becomes smaller.
Thereby, the junction strength and electrical connection reliability between the semiconductor chip and a wiring board or another semiconductor chip are lowered.
Furthermore, if an activator such as a flux is used for removing the oxide film, migration due to impure ions caused by the activator occurs and this may cause an electrical shortcircuit, or nonmetal materials may become mixed in the junction interface between the rear side protruding electrode 82 and the electrode pad or the like and lower the connection reliability.
Furthermore, in the case where a plurality of semiconductor chips 91 are stacked in the thickness direction and the front side protruding electrode 78 and the rear side protruding electrode 82 of two adjacent semiconductor chips 91 are joined to each other, if a stress is applied between these semiconductor chips 91, this stress concentrates in the vicinity of the low melting point metal layer 83 that is the junction portion.
As shown in FIG. 20, in some of the semiconductor chips 91 in which the front side protruding electrodes 78 and the vicinities thereof are made of a metal, such a stress cannot be eased, and the vicinity of the low melting point metal layer 83 that is the joint portion and the vicinity of the interface between the UBM layer 77 and the front side protruding electrode 78 or the interconnection member 81 are broken. Thereby, the mechanical junction and electrical connection between two semiconductor chips 91 are broken in some cases.